feat(core): support ai network search (#9357)

### What Changed?
- Add `PerplexityProvider` in backend.
- Update session prompt name if user toggle network search mode in chat panel.
- Add experimental flag for AI network search feature.
- Add unit tests and e2e tests.

Search results are streamed and appear word for word:

<div class='graphite__hidden'>
          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">录屏2024-12-27 18.58.40.mov</video>

Click the little globe icon to manually turn on/off Internet search:
<div class='graphite__hidden'>
          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">录屏2024-12-27 19.01.16.mov</video>

When there is an image, it will automatically switch to the openai model:

<div class='graphite__hidden'>
          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">录屏2024-12-27 19.02.13.mov</video>

packages/frontend/core/src/desktop/dialogs/setting/general-setting/experimental-features/index.tsx

@@ -105,7 +105,13 @@ const feedbackLink: Record<NonNullable<Flag['feedbackType']>, string> = {
   github: 'https://github.com/toeverything/AFFiNE/issues',
 };
 
-const ExperimentalFeaturesItem = ({ flag }: { flag: Flag }) => {
+const ExperimentalFeaturesItem = ({
+  flag,
+  flagKey,
+}: {
+  flag: Flag;
+  flagKey: string;
+}) => {
   const value = useLiveData(flag.$);
   const t = useI18n();
   const onChange = useCallback(
@@ -128,7 +134,7 @@ const ExperimentalFeaturesItem = ({ flag }: { flag: Flag }) => {
     <div className={styles.rowContainer}>
       <div className={styles.switchRow}>
         {t[flag.displayName]()}
-        <Switch checked={value} onChange={onChange} />
+        <Switch data-testid={flagKey} checked={value} onChange={onChange} />
       </div>
       {!!flag.description && (
         <Tooltip content={t[flag.description]()}>
@@ -175,6 +181,7 @@ const ExperimentalFeaturesMain = () => {
         {Object.keys(AFFINE_FLAGS).map(key => (
           <ExperimentalFeaturesItem
             key={key}
+            flagKey={key}
             flag={featureFlagService.flags[key as keyof AFFINE_FLAGS]}
           />
         ))}

packages/frontend/core/src/desktop/pages/workspace/detail-page/tabs/chat.tsx

@@ -1,9 +1,11 @@
 import { ChatPanel } from '@affine/core/blocksuite/presets/ai';
+import { AINetworkSearchService } from '@affine/core/modules/ai-button/services/network-search';
 import {
   DocModeProvider,
   RefNodeSlotsProvider,
 } from '@blocksuite/affine/blocks';
 import type { AffineEditorContainer } from '@blocksuite/affine/presets';
+import { useFramework } from '@toeverything/infra';
 import { forwardRef, useEffect, useRef } from 'react';
 
 import * as styles from './chat.css';
@@ -20,6 +22,7 @@ export const EditorChatPanel = forwardRef(function EditorChatPanel(
 ) {
   const chatPanelRef = useRef<ChatPanel | null>(null);
   const containerRef = useRef<HTMLDivElement | null>(null);
+  const framework = useFramework();
 
   useEffect(() => {
     if (onLoad && chatPanelRef.current) {
@@ -45,6 +48,13 @@ export const EditorChatPanel = forwardRef(function EditorChatPanel(
       chatPanelRef.current.host = editor.host;
       chatPanelRef.current.doc = editor.doc;
       containerRef.current?.append(chatPanelRef.current);
+      const searchService = framework.get(AINetworkSearchService);
+      const networkSearchConfig = {
+        visible: searchService.visible,
+        enabled: searchService.enabled,
+        setEnabled: searchService.setEnabled,
+      };
+      chatPanelRef.current.networkSearchConfig = networkSearchConfig;
     } else {
       chatPanelRef.current.host = editor.host;
       chatPanelRef.current.doc = editor.doc;
@@ -63,7 +73,7 @@ export const EditorChatPanel = forwardRef(function EditorChatPanel(
     ];
 
     return () => disposable.forEach(d => d?.dispose());
-  }, [editor]);
+  }, [editor, framework]);
 
   return <div className={styles.root} ref={containerRef} />;
 });